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Excellent mechanical properties of long multiwalled carbon nanotube bridged Kevlar fabric
No full textThe major causes of failure of Kevlar reinforced composites are inter-yarn slippage and poor adhesion with polymer. Herein, long length multiwalled carbon nanotubes (MWCNTs) are used as a secondary reinforcement to enhance the interfacial interaction between Kevlar and epoxy through bridging action. Different wt. % of MWCNT based Kevlar reinforced hybrid composite tape and their laminar composites have been prepared and their quasi-static unidirectional and dynamic mechanical properties are studied. It is found that the maximum tensile strength, Young's modulus and storage modulus of optimized i.e. 0.3 wt % of MWCNTs in epoxy resin (0.3KE) composite showed an overall improvement of similar to 81%, similar to 56% and similar to 139%, respectively over base line composite tape (KE). The flexural modulus, Young's modulus and storage modulus of 0.3 wt % multi-scaled laminar composite (KEC) showed an overall improvement of similar to 33%, similar to 50%, and similar to 233%, respectively over KE. The effects of MWCNTs on interfacial properties of multi-scaled composite tapes are correlated by Raman spectral shift, FTIR and XRD analysis. Further the bridging actions of long length MWCNTs are visualized by using high resolution transmission electron microscopy
Elucidating the mechanisms behind thermoelectric power factor enhancement of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) flexible films
No full textConducting polymers that have shown their potential in flexible electronics and sensorics for the last one decade can be looked upon as promising materials for room temperature thermoelectric applications. Among all the existing popular conducting polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is being widely studied because of its extraordinary high electrical conductivity and environmental stability. This article explains the possible mechanisms behind power factor enhancement of solvent-mixed flexible PEDOT:PSS films. The films drop-tasted on polyimide sheets by using both pristine and organic solvent (dimethyl sulphoxide i.e. DMSO) pre-mixed solutions were optimized for both annealing temperature and solvent concentrations. The detailed characterization of these films suggested that PSS was detached from PEDOT:PSS after DMSO addition. Selective eviction of PSS from typical core-shell structure of PEDOT:PSS not only caused conformational change in PEDOT chains from benzoid (coiled structure) to quinoid (linear structure) but also re-arranged PSS in more stretched form. Such a modification of the chemical structure caused improvement in power factor mainly due to enhanced charge carried mobility rather than increased doping/carrier concentration. A flexible thermoelectric generator consisting of an array of thirty elements was also fabricated by drop-casting DMSO-mixed PEDOT:PSS solution through a patterned mask. This array resulted in an output voltage of similar to 17.6 mV under a temperature gradient of 80 degrees C
Transition from n- to p-type conduction concomitant with enhancement of figure-of-merit in Pb doped bismuth telluride: Material to device development
No full textThe majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is similar to 0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of similar to 0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be similar to 4.9% for a temperature difference (Delta T) of 200 K. The efficiency was further enhanced to similar to 12% (at Delta T similar to 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)(0.15)(GeTe)(0.85) (i.e. TAGS-85)
Engineering bright fluorescent nitrogen-vacancy (NV) nano-diamonds: Role of low-energy ion-irradiation parameters
Get PDFBright emission from fluorescent nanodiamonds (FNDs) is highly desirable for optical bio-imaging applications. Here we report about optimized ion-irradiation and heat treatment conditions for efficient creation of Nitrogen-vacancy (NV) centers in high pressure high temperature (HPHT) grown type Ib Nanodiamond samples irradiated in energy range (20-50 KeV) and at varying fluence (10(12)-10(16) ions/cm(2)). Different low energy ion irradiations are not detrimental for the crystallinity of nanodiamonds as confirmed by X-ray diffraction and HRTEM. The concentration of defects near the outer surface (non-diamond carbon) has been increased for highest ion dose (50 KeV, 10(16) ions/cm(2)) as compared to lower ion dose (50 KeV, 10(13) ions/cm(2)). The relative emission intensity of characteristic Zero-phonon lines of NV degrees, NV- centers as compared to broad emission in the range 550-750 nm was monitored with varying NV creation conditions. Sample irradiated at 50 KeV and with fluence of 10(13) ions/cm(2) show maximum emission in the phonon side band (550-750 nm) with maxima at 680 nm. These optimized ion irradiation conditions leads to the fabrication of 12.5 +/- 0.8 ppm concentration of NV- centers in nanodiamonds. This is desirable for their use as biomarker. This work provides a recipe for creating bright nanodiamonds for optical imaging applications
Highly effective adsorption of crystal violet dye from contaminated water using graphene oxide intercalated montmorillonite nanocomposite
No full textHerein, graphene oxide intercalated montmorillonite nanocomposites were prepared by a facile chemical route and then used for the adsorption of crystal violet dye from contaminated water. Structural characterization of the nanocomposites were performed using Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, zeta potential, X-ray diffraction, specific surface area and pore volume measurements. The isothermal data obtained using batch adsorption technique were fitted using Langmuir and Freundlich equations and it was found that the experimental data is well described by the Langmuir isotherm model with a very high adsorption capacity of 746.27 mg g(-1) . The kinetics of the adsorption process showed rapid dynamics and conformed to pseudo-second-order model with a correlation coefficient of R-2 > 0.99. The influence of interaction time and initial dye concentration on the adsorption efficiency were also investigated. Additionally, thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. Further, the results indicated that the synthesised nanocomposites adsorb crystal violet dye efficiently (-96%) with a small decrease in removal efficiency even after five cycles of adsorption and could be employed in wastewater treatment for the removal of cationic dyes
Growth mechanism and optical properties of Ge nanocrystals embedded in a GeO (x) matrix
No full textQuantum confined germanium (Ge) nanocrystals were synthesized by a thermal annealing of germanium oxide thin films fabricated by an e-beam evaporation method. The nanocrystal formation, structure, and sizes upon annealing are evaluated by a combination of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy studies. Spherical nanocrystals with sizes of around 3 nm and having both diamond and tetragonal phases are formed for an annealing temperature of 500 A degrees C. The thermally induced transformation and phase separation of amorphous germanium oxide to nanocrystalline Ge is discussed using X-ray photoelectron spectroscopy. The bandgap agrees with the calculated values using effective mass approximation. The visible photoluminescence is investigated as a function of the annealing temperature. This disproportionation mechanism of germanium oxide films showing favorable optical properties suggests its scope for forming quantum confined Ge nanocrystals embedded in its amorphous matrix relevant for both electronic and optoelectronic applications
Improved magneto-viscoelasticity of cross-linked PVA hydrogels using magnetic nanoparticles
No full textMagnetic nanoparticle (MNP) incorporation in soft host media offers great possibilities to control its properties and flow dynamics via external magnetic field. In the present work we report, synthesis of stable homogeneous crosslinked PVA hydrogels with MNP and their detailed rheological investigations in static and dynamics modes. The measurement results were fitted with the theoretical model presented for nonlinear and transient static & dynamic flow behavior. A good agreement has been observed with theoretical predictions confirming the high dispersivity and stability of these magnetic gels. MNP align themselves in the field direction, and field-induced structures produce hindrance to uniform stress flow which causes a nonlinear viscoelastic response. The substantial enhancement in viscoelastic properties in observed with incorporation of MNP. Static mode investigations show good yielding properties which increases with increase in MNP concentration whereas, dynamic mode storage/loss modulus response shows higher storage modulus than loss modulus. This enhancement indicates the dominance of solid-like nature of magnetic gel due to more significant field-induced structures over applied hydrodynamic forces. These magnetic gels show a quick response to the applied field which is established by transient viscosity response. The viscoelastic properties of these magnetic gels makes it effective and efficient solution for numerous applications in the field of engineering and biomedical
Influence of rare earth ion doping (Ce and Dy) on electrical and magnetic properties of cobalt ferrites
No full textCe and Dy substituted Cobalt ferrites with the chemical composition CoCexDyxFe2-2xO4 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized through the chemical route, citrate-gel auto-combustion method. The structural characterization was carried out with the help of XRD Rieveld analysis, SEM and EDAX analysis. Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. SEM and EDAX results show that the particles are homogeneous with slight agglomeration without any impurity pickup. The effect of RE ion doping (Ce and Dy) on the dielectric, magnetic and impedance studies was systematically investigated by LCR meter, Vibrating Sample Magnetometer and Impedance analyzer respectively at room temperature in the frequency range of 10 Hz-10 MHz. Various dielectric parameters viz., dielectric constant, dielectric loss and ac conductivity were measured. The dielectric constant of all the ferrite compositions shows normal dielectric dispersion of ferrites with frequency. Impedance analysis confirms that the conduction in present ferrites is majorly due to the grain boundary mechanism. Ferrite sample with x = 0.03 show high dielectric constant, low dielectric loss and hence can be utilized in high frequency electromagnetic devices. Magnetization measurements indicate that with increase in Ce and Dy content in cobalt ferrites, the magnetization values decreased and coercivity has increased
Modeling of gate bias controlled NO2 response of the PCDTBT based organic field effect transistor
No full textOrganic field effect transistors consisting of Poly [N-9'-heptadecanyl-2, 7-carbazole-alt-5, 5-(4', 7'-di-2-thienyl- 2', 1', 3'-benzothiadiazole] (PCDTBT) as active layer have been fabricated for detection of gases. The device exhibited highly selective response towards parts-per-million level of NO2 gas. For these devices response towards NO2 decreases with increasing gate bias due to the existing high density of free charges. A model has been developed to explain this variation of response with gate bias using transfer characteristics of the device (in air). This model enables to determine the density of holes released in PCDTBT layer on interaction with NO2 gas
Triluminescent Functional Composite Pigment for Non-Replicable Security Codes to Combat Counterfeiting
No full textHerein, a novel strategy to design of unclonable triluminescent pigment derived security ink is formulated to protect valuable merchandise, bank notes, pharmaceuticals, confidential documents etc. against counterfeiting, by embedding luminescent security codes/images. This triluminescent security ink is designed with combinatory chemistry that involves the strategically admixing of the triluminescent functional composite pigments in commercially available polyvinyl chloride gold medium. The triluminescent functional composite pigment is composed of NaYF4: Yb3+, Er3+(Sodium Yttrium Fluoride doped with Ytterbium and Erbium ions), NaYF4: Eu3+ (Sodium Yttrium Fluoride doped with Europium ion) and ZnO (Zinc Oxide) materials which have multifunctional features as it looks white in ambient light and shows strong green (NaYF4: Yb3+, Er3+), red (NaYF4: Eu3+) and green (ZnO) colors at three different excitations of 980 nm, 254 nm and 379 nm wavelengths, respectively. The structural/microstructural and photoluminescence properties of triluminescent functional composite are confirmed by XRD (X-ray diffraction), SEM (Scanning electron microscope), TEM (Transmission electron microscope) and photoluminescence spectroscopic techniques, respectively. The quality and spatially distributed PL intensity of printed images/code from triluminescent ink was investigated by photoluminescence confocal mapping microscopy technique. Hence, the obtained results suggest that the security code/images printed by using ink formulated from triluminescent functional composite pigment provides one step ahead novel security features which could be easy to detect but extremely difficult to replicate